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The 20-acre East Bay hills vegetation fire that broke out early Wednesday afternoon is now 70 percent contained. Firefighters hope to have it 90 percent contained by the end of the day Friday, Oakland fire Battalion Chief Melinda Drayton said.

Less than 50 firefighters from four agencies are still fighting the blaze, which was reported at 1:05 p.m. on Wednesday near Grizzly Peak Boulevard and South Park Drive, Drayton said.

That contrasts with the approximately 200 firefighters who were at the scene at the height of the fire on Wednesday afternoon.

Half of the fire was on Oakland land in the hills and half of the fire was on land owned by the Lawrence Berkeley National Laboratory that's mostly in Contra Costa County, according to Drayton.

Firefighters will remain at the scene overnight and into Saturday to make sure that the blaze becomes completely extinguished, she said.

University of California at Berkeley police spokeswoman Sgt. Sabrina Reich said on Thursday that the fire is being considered as a possible arson but Drayton has declined to comment on that, saying that Cal Fire is the lead investigative agency looking into the cause and origin of the fire.

Cal Fire Battalion Chief Mike Martin said at the scene late Thursday afternoon that the only thing he can say is that there's an open investigation into the fire and the probe could take days, weeks or even months.

Also on Thursday, Oakland police said UC Berkeley officers

arrested a person who fled the scene of a collision on Grizzly Peak Boulevard that occurred Wednesday morning, near where the fire began. Police haven't said whether that incident is related to the blaze.

An Oakland police spokesman declined to release the suspect's name Friday, saying that there's still an active investigation into the matter and police aren't releasing any additional information at this time.

Fire officials said Grizzly Peak Boulevard between Centennial and South Park Drive is expected to remain closed until 8 p.m. Friday but it's possible that it could reopen earlier if conditions allow.